Fix Prism API name: highlightElem -> highlightElement

The article's prose and inline examples use Prism.highlightElem, which
does not exist in the Prism.js API, while the demo code later in the same
article correctly uses Prism.highlightElement. Unify on the real API name.

Also pass only the element in forEach callbacks: forEach supplies
(element, index, array), which would collide with the
highlightElement(element, async, callback) signature if the method
reference is passed directly.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MizgRqMWEBSTYhJ9YhSd2g

Author: Violet-Bora-Lee

2-ui/99-ui-misc/01-mutation-observer/article.md

@@ -128,13 +128,13 @@ Such snippet in an HTML markup looks like this:
 ...
 ```
 
-For better readability and at the same time, to beautify it, we'll be using a JavaScript syntax highlighting library on our site, like [Prism.js](https://prismjs.com/). To get syntax highlighting for above snippet in Prism, `Prism.highlightElem(pre)` is called, which examines the contents of such `pre` elements and adds special tags and styles for colored syntax highlighting into those elements, similar to what you see in examples here, on this page.
+For better readability and at the same time, to beautify it, we'll be using a JavaScript syntax highlighting library on our site, like [Prism.js](https://prismjs.com/). To get syntax highlighting for above snippet in Prism, `Prism.highlightElement(pre)` is called, which examines the contents of such `pre` elements and adds special tags and styles for colored syntax highlighting into those elements, similar to what you see in examples here, on this page.
 
-When exactly should we run that highlighting method? Well, we can do it on `DOMContentLoaded` event, or put the script at the bottom of the page. The moment our DOM is ready, we can search for elements `pre[class*="language"]` and call `Prism.highlightElem` on them:
+When exactly should we run that highlighting method? Well, we can do it on `DOMContentLoaded` event, or put the script at the bottom of the page. The moment our DOM is ready, we can search for elements `pre[class*="language"]` and call `Prism.highlightElement` on them:
 
 ```js
 // highlight all code snippets on the page
-document.querySelectorAll('pre[class*="language"]').forEach(Prism.highlightElem);
+document.querySelectorAll('pre[class*="language"]').forEach(elem => Prism.highlightElement(elem));
 ```
 
 Everything's simple so far, right? We find code snippets in HTML and highlight them.
@@ -146,9 +146,9 @@ let article = /* fetch new content from server */
 articleElem.innerHTML = article;
 ```
 
-The new `article` HTML may contain code snippets. We need to call `Prism.highlightElem` on them, otherwise they won't get highlighted.
+The new `article` HTML may contain code snippets. We need to call `Prism.highlightElement` on them, otherwise they won't get highlighted.
 
-**Where and when to call `Prism.highlightElem` for a dynamically loaded article?**
+**Where and when to call `Prism.highlightElement` for a dynamically loaded article?**
 
 We could append that call to the code that loads an article, like this:
 
@@ -158,7 +158,7 @@ articleElem.innerHTML = article;
 
 *!*
 let snippets = articleElem.querySelectorAll('pre[class*="language-"]');
-snippets.forEach(Prism.highlightElem);
+snippets.forEach(elem => Prism.highlightElement(elem));
 */!*
 ```